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Rare Moon Mineral Found on Earth

Posted: January 6th, 2012 | Author: | Filed under: Applied Science, Cankler Science News, Geology | Tags: , , , , , , , , , | Comments Off on Rare Moon Mineral Found on Earth

NASA Apollo 8 - December 24, 1968 - EarthriseA mineral brought back to Earth by the first men on the Moon and long thought to be unique to the lunar surface has been found in Australian rocks more than 1 billion years old. In this month’s issue of Geology, Birger Rasmussen, a geologist at Curtin University in Australia, and his colleagues report that they’ve finally found tranquillityite on our planet.   Named after Apollo 11’s 1969 landing site at the Sea of Tranquility, tranquillityite was one of three minerals first discovered in rocks from the Moon and the only one not to be found, in subsequent years, on Earth.

The West Australian mineral was dated at 1.07 billion years old, more ancient than rocks in the area had previously been thought to be, Rasmussen said tranquillityite would be useful in dating similar rocks in the future.”They were always part of Earth. They haven’t come from the Moon,” Rasmussen said

The discovery has important practical applications, with the mineral proving to be an excellent dating tool which had allowed scientists to pin down the rocks’ ages. “We used this mineral… to date the dolerite which has previously been undated, so that helped us understand the geological history,” Rasmussen said. “It tells you that broadly overall you have similar chemistries and similar processes operating on the Moon as on Earth.”

 Lunar Libration With Phase October 2007

Rare Moon Mineral Found in Australia

Rasmussen said tranquillityite had “long been considered as the Moon’s own mineral” until geologists discovered it, by chance, in rock from resources-rich Western Australia.Tranquillityite is silicate mineral with an average formula (Fe2+,Ca)8(Zr,Y)2Ti3 – (SiO4)3O4. It is mostly composed of iron, oxygen, silicon, zirconium and titanium with smaller fractions of yttrium and calcium. It is named after the Mare Tranquillitatis – Sea of Tranquility – the place on the Moon where it was found during the Apollo 11 and 12 missions in 1969. It was identified in 1971 and later found in lunar rocks from all Apollo missions.

When the Moon samples first came back, Dr Rasmussen said they were considered to be “extremely precious” and had been subjected to intense, detailed study when, ironically, their contents were “right here all the time”. “In over 40 years it hadn’t been found in any terrestrial samples,” said Rasmussen.

Tranquillityite forms thin stripes up to 15 by 65 micrometres in size in basaltic rocks, where it was produced at a late crystallization stage. It is associated with troilite, pyroxferroite, cristobalite and alkali feldspar. The mineral is nearly opaque and appears dark red-brown in thin crystals. It usually contains minor impurities of Al, Mn, Cr, Nb and rare-earth elements (parts per million), as well as up to 0.01% of uranium. Presence of significant amount of uranium allowed to estimate the age of moon sourced tranquillityite and some associated minerals in Apollo 11 samples as 3710 million years using the uranium-lead dating technique.

The West Australian mineral was dated at 1.07 billion years old, more ancient than rocks in the area had previously been thought to be, Rasmussen said tranquillityite would be useful in dating similar rocks in the future.”They were always part of Earth. They haven’t come from the Moon,” Rasmussen said

The discovery has important practical applications, with the mineral proving to be an excellent dating tool which had allowed scientists to pin down the rocks’ ages. “We used this mineral… to date the dolerite which has previously been undated, so that helped us understand the geological history,” Rasmussen said. “It tells you that broadly overall you have similar chemistries and similar processes operating on the Moon as on Earth.”

“Tranquillityite is not that unique in its overall chemistry, so it’s odd that it hadn’t been found in Earth rocks before,” Rasmussen says. Nevertheless, he notes, the mineral likely remained elusive for several reasons. First, typical bits of tranquillityite—which are shaped like tiny needles that have been pounded flat—are unusually small, about 150 micrometers long, or slightly less than the diameter of the thickest human hair. Second, lunar rocks are more pristine than those on Earth, which are much more likely to have been altered either chemically, by hot fluids rich in dissolved minerals flowing through them, or physically, by geological processes such as plate tectonics, which can carry rocks deep below Earth’s surface and subject them to hellish temperatures and pressures. Finally, Rasmussen says, tranquillityite can easily be mistaken for rutile, a similarly colored mineral commonly found in igneous rocks. Only certain types of analyses, such as the electron diffraction analyses conducted by the team, can discern tranquillityite, and samples of Earth rocks typically don’t get such detailed scrutiny, he notes. “The lunar samples were so precious, they were studied in great detail,” Rasmussen said.

Rasmussen’s team looked at igneous rocks of Western Australia, particularly those that didn’t show signs of having undergone large-scale metamorphic changes deep within Earth. That’s because when tranquillityite is exposed to excessive heat and pressure, it readily transforms into other minerals. The team confirmed the presence of the mineral by firing high-speed electrons through tiny rock samples. They noted that the flecks of tranquillityite scattered the electrons in a distinctive pattern matching that produced by lunar samples of the mineral.

Rasmussen says the fact that tranquillityite has now been found in six widely scattered sites in Western Australia suggests that it might be more common than thought.

source: geology

source: science now


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